Blunted IgE-mediated activation of mast cells in mice lacking the Ca ²⁺-activated K⁺ channel K_Ca3.1

Mast cell stimulation by Ag is followed by the opening of Ca ²⁺-activated K⁺ channels, which participate in the orchestration of mast cell degranulation. The present study has been performed to explore the involvement of the Ca²⁺-activated K⁺ channel K_Ca3.1 in mast cell function. To this end mast cells have been isolated and cultured from the bone marrow (bone marrow-derived mast cells (BMMCs)) of K_Ca3.1 knockout mice (K_Ca3.1^-1-) and their wild-type littermates (K_Ca3.1^+/+). Mast cell number as well as in vitro BMMC growth and CD117, CD34, and FcεRI expression were similar in both genotypes, but regulatory cell volume decrease was impaired in K_Ca3.1^-1- BMMCs. Treatment of the cells with Ag, endothelin-1, or the Ca²⁺ ionophore ionomycin was followed by stimulation of Ca²⁺-activated K⁺ channels and cell membrane hyperpolarization in K_Ca3.1^+/+, but not in K _Ca3.1^-1- BMMCs. Upon Ag stimulation, Ca²⁺ entry but not Ca²⁺ release from intracellular stores was markedly impaired in K_Ca3.1^-1- BMMCs. Similarly, Ca²⁺ entry upon endothelin-l stimulation was significantly reduced in K_Ca3.1 ^-1- cells. Ag-induced release of β-hexosaminidase, an indicator of mast cell degranulation, was significantly smaller in K_Ca3.1 ^-1- BMMCs compared with K_Ca3.1^+/+ BMMCs. Moreover, histamine release upon stimulation of BMMCs with endothelin-l was reduced in K_Ca3.1^-1- cells. The in vivo Ag-induced decline in body temperature revealed that IgE-dependent anaphylaxis was again significantly (by ∼50%) blunted in K_Ca3.1^-1- mice. In conclusion, K_Ca3.1 is required for Ca²⁺-activated K ⁺ channel activity and Ca²⁺-dependent processes such as endothelin-1- or Ag-induced degranulation of mast cells, and may thus play a critical role in anaphylactic reactions.